1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming apparatus and an image forming method of forming an image by ejecting droplets of ink after depositing a treatment liquid which aggregates or insolubilizes the ink onto the front surface of a recording medium.
2. Description of the Related Art
In an inkjet recording apparatus which forms an image on a recording medium by ejecting droplets of ink, problems such as feathering or bleeding occur when an image is formed on so-called normal paper.
Therefore various technologies for preventing the occurrence of feathering or bleeding have been proposed. One of these is a known method of forming an image by ejecting ink droplets after previously depositing a treatment liquid which aggregates or insolubilizes ink onto the front surface of paper. This method insolubilizes the coloring material and/or raises the viscosity by causing a reaction of some kind with the ink, but the insoluble material or raised viscosity components arising from this reaction remain on the front surface of the paper and this gives rise to problems, for instance, the density distribution of the recorded image becomes non-uniform, or permeation into the paper of the solvent or water contained in the ink is obstructed and hence the fixing time of the image becomes long.
Therefore, as a method for resolving this problem, Japanese Patent Application Publication No. 2004-291627 discloses a method in which paper is conveyed while being suctioned on a conveyance belt in which suction holes (air holes) are formed, treatment liquid is deposited onto the paper suctioned and conveyed on the conveyance belt by a treatment liquid deposition device, and ink is then deposited from a recording head.
If paper is suctioned during conveyance as in Japanese Patent Application Publication No. 2004-291627, the paper is recessed in the portions corresponding to the suction holes, and if treatment liquid is deposited by application with a roller, or the like, the treatment liquid moves to these recess portions (recesses), and is liable to collect there. Furthermore, if treatment liquid is deposited by ejection from a recording head, or the like, there is a possibility that deviation occurs in the depositing positions at the recess portions. Furthermore, since the suctioning force in the portions corresponding to the suction holes is stronger than in other portions, the permeation of treatment liquid is accelerated at the perimeter of the suction holes only, and as a result of this, non-uniformity occurs in the treatment liquid density, and hence image non-uniformities arise.
Problems of this kind can be eliminated to a certain degree by adjusting the suctioning force during suction and conveyance, but if the paper is conveyed on the same conveyance belt from the deposition of treatment liquid until the deposition of ink and ink deposition is carried out consecutively following the deposition of treatment liquid, as in Japanese Patent Application Publication No. 2004-291627, then the deposition non-uniformities of the treatment liquid and the deposition non-uniformities of the ink are mutually superimposed (the non-uniformities due to the suctioning force are doubled) and therefore the image non-uniformities become worse.